Method and arrangement for monitoring the operating condition of presses, particularly packing presses

ABSTRACT

The aim of the invention is to monitor the operating condition of a press, especially a packing press ( 1 ) while preventing the machine parts that are involved in the relative movements from fretting. Said aim is achieved by a) detecting amplitudes of vibrations during the time and/or a distance of a relative movement occurring between at least one compressor ( 3.1, 3.2, 3.3 ) and/or a door ( 5.1 ) and the press case ( 2.2 ) within a cycle that lasts from the beginning to the end of the compression process and the ejection of the pressed article, and predefining an admissible oscillation amplitude of the entire press within the control mechanism ( 16.2 ) as a “normal condition” for increments of the duration and/or the distance of the relative movements; b) generating an “alert value” lying above the maximum value established for the normal condition and a shut-off value lying above the alert value; c) inputting both threshold values of the alert value and the shut-off value in the control mechanism ( 16.2 ) of the press ( 1 ) for each relevant relative movement or each increment of the duration and/or the distance of the relative movement; and d) controlling operation of the press during the cycle lasting from the beginning to the end of the compression process or during the relevant relative movement by means of the control mechanism ( 16.2 ), a signal being displayed when the alert value and/or the shut-off value has/have been reached.

TECHNICAL FIELD

The invention relates to a method and an arrangement for monitoring theoperating condition of presses, particularly packing presses for theproduction of pressed objects, such as from scrap and sheet metalwastes.

PRIOR ART

For example, shear packing presses according to DE 198 04 789 are known,which substantially comprise a hopper with cutting edge, compactor withshearing knives guided horizontally therein, a press case arranged atright angles thereto with compactor guided therein and a pack chamber,arranged horizontally and transversely with respect to the hopper andwith a compactor guided horizontally.

In practical embodiments, hopper and press case open into a commonchamber accommodating the pack-like pressed object, the aforementionedpack chamber. The walls of the hopper, press case and pack chamber formthe housing of the shear packing press. The pack chamber has an openingfor the door to be displaced horizontally, through which the ejectedpressed object passes. The compactor and the door are moved by hydraulicpistons/cylinders, which are connected to a hydraulic drive system.

To produce pressed objects, preferably packs, from waste material, inparticular from scrap and sheet metal wastes, by means of such knownshear packing presses

-   -   a first compaction step for the pre-compaction of the material        put in to the width of the pack is carried out by means of a        compactor guided horizontally in the hopper, material possibly        projecting beyond the compactor being cut off at the cutting        edge by means of the shearing knife arranged on the compactor,    -   after that, a second compaction step for the intermediate        compaction of the material pre-compacted to the pack width to        the height of the pack is carried out by means of the compactor        guided in the press case at right angles to the hopper,    -   then, a third compaction step for the final compaction of the        material to the final density and length of the pack is carried        out by means of the compactor guided horizontally in the pack        chamber, horizontally and transversely with respect to the        hopper, the finished pack, after reaching the final density and        length, being ejected from the pack chamber through the door,        and    -   finally, the control of these compaction steps is carried out by        means of a drive system producing a hydraulic pressure.

This basic principle has proven worthwhile in practice but there is arequirement for functional improvements with regard to monitoring theoperating condition of presses.

In this case, presses are not just understood to mean the type mentionedat the beginning. In the sense of the invention, the requirement for animprovement in the monitoring of the operating condition extends only asfar as presses, i.e. machines, in which, because of the relativemovement between a driven compactor and a press case or table absorbingthe compaction pressure for the pressed object, what is known as astick-slip effect occurs. This applies to presses that actone-dimensionally, two-dimensionally and also three-dimensionally(specifically of the type mentioned at the beginning).

In presses, this stick-slip effect because of the friction between thesurfaces of the machine parts involved sliding on one another isexpressed by chattering and/or creaking noises. The cause of this isthat, during the aforementioned relative movement, under the action ofthe relatively high pressures and components turning away from theactual pressing direction, the movement changes from adhesive frictionto moving friction and vice versa. The acoustically perceivableoscillations which are therefore produced are in turn produced by thefact that the entire machine, in particular the machine partrespectively involved, is set oscillating.

In the extreme case, as a result of a high-frequency frictionalmovement, the frictional surface respectively involved can weld locally,which is generally designated “fretting”. For the machine, this meansconsiderable damage, which can be rectified only with considerableeffort. Furthermore, a loss of production arises for the operator, whichleads to consequential damages.

SUMMARY OF THE INVENTION

The invention has the object of developing a method and an arrangementfor monitoring the operating condition of presses, in particular packingpresses, damaging oscillation stresses being detected in good time and“fretting” of the machine parts involved in the relative movements beingavoided.

According to the invention, this object is achieved by the features ofclaims 1 to 12.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows the schematically illustrated arrangement according to theinvention using the example of a packing press, in a perspectiveillustration,

FIG. 2 shows a plan view with a schematically illustrated arrangementaccording to the invention.

BEST WAY OF IMPLEMENTING THE INVENTION

The invention will be explained in terms of its basic arrangement andthe active principle on a packing press operating three-dimensionally,in accordance with the following exemplary embodiment.

According to FIG. 1, the packing press 1 substantially comprises a presscase 2.2 and a pack chamber 2.3, and a first compactor 3.1 driven by afirst piston/cylinder unit 6.1, and a second compactor 3.2 driven by asecond piston/cylinder unit 6.2 and a third compactor 3.3 driven by athird piston/cylinder unit 6.3 (FIG. 2 a). A door 5.1 connected to afourth piston/cylinder unit 6.4 is guided in a door case 5.2 such thatit can be moved horizontally. The door case 5.2 is fixed to the housingpart of the pack chamber 2.3 by means of a tie rod 10, the tie rod 10 atthe same time absorbing the pressure against the door 5.1 exerted on apressed object, not illustrated, by the third piston/cylinder unit 6.3by means of the third compactor 3.3.

In accordance with the erection possibility illustrated in FIG. 2 for ahydraulic drive system 9.1 of the packing press 1, said systemsubstantially comprises a control block 9.2, a hydraulic tank 13 and aswitch cabinet 16, which form a compact structural unit which can bepreassembled on its own. With the switch cabinet 16 is a controller16.2, which is connected via a connecting cable 16.4, a charge amplifier(coupler) 16.1 and a dimension line 16.3 to a sensor 2.4 on an end wallof the press case 2.2 of the packing press 1.

The following basic series of steps or sequences and combinations aretypical of the operation of the packing press 1:

-   -   the pre-compaction of the material by means of the first        compactor 3.1 in the first compaction step,    -   the following second compaction step by means of the second        compactor 3.2,    -   the third compaction step, carried out by means of the third        compactor 3.3, in which the first compactor 3.1 is already in a        position exposing the opening of the pack chamber 2.3.

In this case, the return strokes of the compactors 3.1, 3.3 can becoupled, the compactor 3.3 then initially covering part of the distanceon its own and the remainder of the distance together with the compactor3.1.

The door 5.1 is closed at the same time as the return stroke of thethird compactor 3.3 by means of hydraulic isolation, or opened at thesame time as the return stroke of the compactor 3.2 by means ofhydraulic isolation.

For all these sequences, use is made of a controller 16.2, whichmonitors the movement sequences of the compactors 3.1, 3.2, 3.3 and thedoor 5.1 during the cycles for the production of the pressed object, notillustrated.

These movements sequences of the compactors 3.1, 3.2, 3.3 and of thedoor 5.1, specifically with the involvement of relatively high forces,in critical positions produce the undesired stick-slip effect alreadydescribed in more detail at the beginning which, according to theobject, is to be detected in good time in order to avoid “fretting” ofthe machine parts involved in the movement sequences.

By means of the arrangement of the controller 16.2, which isconstructionally relatively simple but surprising in its effect, withthe sensor 2.4 fitted to the end wall of the press case 2.2 formeasuring oscillation amplitudes, the measuring line 16.3 for passing onthe measured values with a coupler as charge amplifier 16.1 and aconnecting cable 16.4, the method according to the invention is carriedout as follows.

Relative movements taking place during the time and/or distance betweeneach compactor 3.1, 3.2, 3.3 and the press case 2.2 and also the door5.1 in the cycle from the start until the end of the pressing operationand the ejection of the pressed object, not illustrated, the oscillationamplitudes are registered continuously via the sensor 2.4. After that, apermissible oscillation amplitude for the packing press 1 is registeredwithin the controller 16.2 as a “normal condition” for the time and/ordistance increments of the relative movements.

Then, an “alarm value” with a magnitude 20% higher than the maximummeasured value of the oscillations in the normal condition is generated,and a “shut-off value” having a magnitude 40% higher than the previousmaximum measured value is generated and the two limiting values areentered into the controller 16.2 of the press 1 for each time and/ordistance increment, with the effect of an incremental memory.

The operation of the press is ultimately managed, completing the seriesof steps according to the invention, by the use of a program integratedinto the controller 16.2, in such a way that

-   -   a) in a learning phrase, the maximum oscillation amplitudes        during the various relative movements belonging to the pressing        cycle or the movement increments are recorded,    -   b) automatic generation of the “alarm” and “shut-off values” is        carried out,    -   c) in the actual active phase, the measured values of the        oscillation amplitudes during the pressing operation are        registered and compared continuously with the respective        associated “alarm and shut-off values” belonging to the distance        and/or time increment,    -   d) appropriate actions are triggered automatically if the values        are exceeded.

The idea of an incremental memory is used completely in the system formonitoring the operating condition of the packing press in order toachieve the object, namely the prevention of “fretting” of relevantmachine parts, in that “alarm” or “stop” are triggered automaticallywhen a current measured value goes beyond a tolerance value.

It is expedient to indicate the values “normal condition”, “alarm value”and “shut-off value” on a monitor, not designated, of an operatorguidance system in the controller 16.2 of the packing press 1.

COMMERCIAL APPLICABILITY

Although its effect is associated with substantially increasedserviceability for the operator of machines of the generic type, theinvention may be implemented with relatively simple means, evenretrofitting according to the invention of presses already in operationbeing unproblematic.

LIST OF DESIGNATIONS

-   1=Shear packing press-   2.1=Hopper-   2.2=Press case-   2.3=Pack chamber-   2.4=Sensor-   3.1=First compactor-   3.2=Second compactor-   3.3=Third compactor-   5.1=Door-   5.2=Door case-   6.1=First piston/cylinder unit-   6.2=Second piston/cylinder unit-   6.3=Third piston/cylinder unit-   6.4=Fourth piston/cylinder unit-   9.1=Hydraulic drive system-   9.2=Control block-   10=Tie rod-   13=Hydraulic tank-   16=Switch cabinet-   16.1=Coupler/charge amplifier-   16.2=Controller-   16.3=Measuring line-   16.4=Connecting cable

1. A method for monitoring the operating condition of a press,particularly a packing press (1), for the production of pressed objects,preferably packs made from waste material, in particular from scrap andsheet metal wastes, comprising at least one step which can be registeredby measurement in terms of time and/or distance for compacting thematerial put in in a press case (2.2) a step which can be registered bymeasurement in terms of time and/or distance for ejecting the finishedpack or pressed object, and a controller (16.2) for carrying out thesesteps by means of a drive system (9.1) producing a hydraulic pressure,and registration of amplitudes of the oscillation condition of the pressand predefinition of at least one permissible oscillation amplitude as areference value for the controller (16.2) of the press (1),characterized by a) registration of the amplitudes of oscillationsduring the time or a distance of a relative movement taking placebetween at least one compactor (3.1, 3.2, 3.3) and/or machine elementsuch as a door (5.1) and the press case (2.2) in the cycle from thestart until the end of the pressing operation, and also ejection of thepressed object and predefinition of a permissible oscillation amplitudeof the entire press within the controller as a “normal condition” fortime or distance increments of the relative movements, b) generation ofan “alarm value” with a magnitude which is above the maximum value inthe “normal condition”, and generation of a “shut-off value” with amagnitude which is above the “alarm value”, c) entry of both limitingvalues from “alarm value” and “shut-off value” for each relevantrelative movement or for each time or distance increment of the relativemovement into the controller of the press (1) and d) operation of thepress by means of the controller (16.2) with indication of a signal whenthe “alarm value” is reached and/or the “shut-off value” is reachedduring the cycle from the start until the end of the pressing operationor the relevant relative movement.
 2. The method as claimed in claim 1,characterized in that the “alarm value” to be generated lies below thevalue of the amplitude which causes the stick-slip effect triggeringfretting of the machine parts involved in the relative movement, so thatno alarm is reported during fault-free operation.
 3. The method asclaimed in claim 1, characterized in that the “shut-off value” to begenerated lies below the value of the amplitude which causes thestick-slip effect triggering fretting of the machine parts involved inthe relative movement.
 4. The method as claimed in claim 1,characterized in that the amplitudes of the oscillations within thecycle of a relative movement of the machine parts involved in thepressing and ejection operation are registered while excludingnon-critical oscillation amplitudes of other machine parts, and afterthat the values “normal condition”, “alarm value” and “shut-off value”are stored in the controller (16.2).
 5. The method as claimed in one ofclaims 1 to 4, characterized in that the oscillation amplitudes aremeasured only during the movement of at least one of the piston/cylinderunit (6.1, 6.2, 6.3) acted on by a hydraulic drive system (9.1).
 6. Themethod as claimed in one of claims 1 to 4, characterized in that whenthe “alarm value” and/or the “shut-off value” is reached, the operationof the press can be switched off automatically.
 7. The method as claimedin one of claims 1 to 6, characterized in that the oscillationamplitudes are measured by means of a sensor (2.4) fixed to an exposedpoint of the press case (2.2).
 8. The method as claimed in one of claims1 to 7, characterized by the use of an integrated program for thecontroller (16.2) of the press, the program comprising the steps of a) alearning phase with recording of the maximum oscillation amplitudeduring the various relative movements belonging to the pressing cycle orthe relative movement increments, b) automatic generation of alarm andshut-off values, c) an active phase with registration of the measuredvalues of the oscillation amplitudes during the pressing operation andcontinuous comparison with the respective alarm and shut-off valuesbelonging to the distance or time increment and automatic triggering ofappropriate actions if alarm and shut-off values are exceeded.
 9. Themethod as claimed in one of claims 1 to 8, characterized in that the“alarm value” is set to be an order of magnitude around 20% higher thanthe maximum measured value of the oscillations in the “normalcondition”, and the “shut-off value” is set to be an order of magnitudearound 40% higher than the measured value of the oscillations in the“normal condition”, and are entered into the program for the control ofthe press (16.2).
 10. An arrangement for monitoring the operatingcondition of presses in order to carry out the method as claimed inclaim 1 to 9, comprising the controller (16.2), at least one sensor(2.4) fitted to an exposed point of the press case (2.2) for measuringthe oscillation amplitudes, a measuring line (16.3) for passing on themeasured values with a coupler as charge amplifier (16.1), and aconnecting cable.
 11. The arrangement as claimed in claim 10,characterized in that the sensor (2.4) is fitted to an end of the presscase (2.2).
 12. The arrangement as claimed in claim 10, characterized inthat the values “normal condition”, “alarm value” and “shut-off value”can be indicated on a monitor of an operator guidance system in thecontroller (16.2) of the packing press.